Supermodel Erin O'Connor slams designers for trying to brainwash women with a fantasy image not attainable without digital trickery.

On the eve of London Fashion Week, Erin O'Connor - described by Karl Lagerfeld as "one of the best models in the world" - had a confession to make. "I'm a fashion model and I don't fit into the sample sizes. I haven't for some time. At one show I couldn't get into the trousers. The designer said, 'What happened to you?' I replied,'Why don't you make your trousers bigger?"'

She described herself as being made to feel like a "commodity". "Fashion is built on perpetuating fantasy. There is a sense of uniformity. We have forgotten how to be individuals."

O'Connor was speaking alongside Britain's equalities minister Lynne Featherstone at a debate for All Walks Beyond the Catwalk, an ambitious event held over three floors of the National Portrait Gallery in London. The aim? To stamp out "the dominance of a singular aesthetic", or fashion's obsession with youth, perfection and size zero.

The latest target? Airbrushing and trickery in advertising. Several key players called for industry regulation with various ideas proposed: kite-marking to indicate digital tampering, or a "golden star" system for natural images.

Organiser Caryn Franklin, the one-time BBC Clothes Show presenter, led the attack: "We must question the manipulation of imagery." Many magazine editors have told her, off the record, that they are concerned the culture of digital enhancement is getting out of control. "They wish there were guidelines for dealing with photographers who ingratiate themselves with celebrities by creating the most polished of shots."

On view for one night only was Rankin's Snapped, a photographic collection of models of all sizes and ages in creations by Vivienne Westwood, Stella McCartney, Matthew Williamson and other British designers, all inspired by portraits in the gallery. An estimated 3000 visitors turned up, marking the unofficial opening of London Fashion Week.

During fashion week, O'Connor also opens the doors of her "models' sanctuary" in London's Covent Garden for the fourth year running. This is a non-profit, drop-in centre visited by more than 200 models a day during the shows, where they can seek advice from nutritionists, life coaches and physiotherapists. "Ninety per cent of models are aged 16 to 19. As an industry we have to take responsibility for them," said O'Connor.

On the debate's stage, the predominant colour was regulation fashion uniform: black. Apart from the Christian Louboutin red-soled shoes worn by Elle editor Lorraine Candy.

She opposes regulation: "We're not a charity. We're producing what women want. If they didn't want it, they wouldn't buy it."

She said, however, that she had recently rejected "a very famous young Hollywood celeb" for a cover shoot because she had had too much plastic surgery.

"It was unrealistic to make my readers feel they should look like that."

Since All Walks was set up in 2009 by O'Connor, Franklin and fashion PR Debra Bourne, more voluptuous models and older women have appeared on the catwalk, most recently at Prada and Louis Vuitton. Tackling digital enhancement is next.

"Women believe these images are real," said panel member Kiki Kendrick, the advertising guru who came up with the "size 16 Barbie" for the Body Shop. "That is what happened with the girl who had herself injected with silicone," she added, referring to 20-year-old British tourist Claudia Seye Aderotimi, who died in Philadelphia recently after a "buttock enhancement" operation arranged over the internet went wrong.